Glyceride oil refining processes

ABSTRACT

Glyceride oils are refined by treatment with aqueous alkali in the presence of from 3 to 15 percent by w/w preferably 4 to 97 percent on the aqueous phase of alkali metal, alkaline earth metal or ammonium salt of a phenyl or alkylphenyl sulphonic acid containing not more than 3 alkyl substituents having not more than 4 carbon atoms in the aggregate; the molar ratio of sulphonate to soap present in from 0.1 : 1 to 1:1, preferably 0.25:1 to 0.5:1. The aqueous soapstock layer containing sulphonate is separated and may be acidified to recover free fatty acids. The remaining aqueous sulphonate material may be discarded or recycled to the refining stage.

llliited States Patent Marsden et al.

[ GLYCERIDE OIL REFINING PROCESSES [76] Inventors: Frank Charles Marsden, Priory Rd., St. Bees; John Maden, 1O Highfield Ct.; Paul Frederick Flanagan, 10 Standings Rise, all of Cumberland, England 22 Filed: May4, 1971 21 Appl. No.: 140,231

[30] Foreign Application Priority Data OTHER PUBLICATIONS Chem. Abstracts, Vol. 67, 1967, 91987K.

[ Dec. 24, 1974 Primary Examiner-Lewis Gotts Assistant ExaminerEthyl G. Love Attorney, Agent, or Firm-Herbert H. Goodman [57] ABSTRACT Glyceride oils are refined by treatment with aqueous alkali in the presence of from 3 to 15 percent by w/w preferably 4 to 97 percent on the aqueous phase of alkali metal, alkaline earth metal or ammonium salt of a phenyl or alkylphenyl sulphonic acid containing not more than 3 alkyl substituents having not more than 4 carbon atoms in the aggregate; the molar ratio of sulphonate to soap present in from 0.1 1 to 1:1, preferably 0.25:1 to 0.511. The aqueous soapstock layer containing sulphonate is separated and may be acidified to recover free fatty acids. The remaining aqueous sulphonate material may be discarded or recycled to the refining stage.

7 Claims, N0 Drawings ll GLYCERllDE OIL REFINING PROCESSES This invention concerns glyceride oil refining processes wherein a glyceride oil is treated with aqueous alkali in the presence of an aryl or lower alkyl aryl sulphonic acid.

A number of such processes are known, e.g. as described in U.K. Pat. Nos. 1,002,974; 1,077,557; French Pat. No. l,454,709; West German OLS Nos. 18 08 443 and 17 67 8l4and U.S. Pat. No. 3,440,253. in all of these the admixture of the crude oil with aqueous alkali and sulphonate salt produces a two phase system comprising an oily layer and an alkaline soapstock layer containing dissolved sulphonate salt. These layers are separated and the oily layer worked up as product whilst the aqueous layer is acidified with sulphuric acid to separate free fatty acids therefrom and is then recycled to the refining stage since it contains sulphonate salt. Such recycling is by no means straight forward since there is a need to purge sodium sulphate arising from the alkali .used in the refining stage and the acid used in the acidification stage. Purging is most readily accomplished by evaporative cystallization but the crystal size of sodium sulphate removable in this way is extremely sensitive to'impurities in the mother liquor, especially traces of soaps and glyceride oil. As a consequence filtration of crystallized sodium sulphate from the aqueous recycle stream can be difficult unless, fairly elaborate precautions are taken. (See, e.g., copending U.K. application Ser. No. 22, l 64/70, now British Pat. No. l ,307,862).

Heretofore it has been generally assumed that the ac- I tion of the sulphonate salts in this process was a hydrotropic phenomenon, i.e., an effect by which high aqueous concentrations of the dissolved sulphonate salt solubilised the otherwise sparingly soluble soap. This was borne out by the practical observation that refining in the absence of sulphonate salt produced a difficulty separable phase system in which the aqueous layer contained large amounts of occluded glyceride oil apparently solvated by miceller soap solutions. Refining in the presence of appreciable quantities of sulphonate, however, produced two distinct phases which readily disengaged. Accordingly all previous literature describing the use of aryl or lower alkyl aryl sulphonate salts to encourage phase separation in the alkaline refining of glyceride oil has recommended that the aqueous concentration of sulphonate salt be at or above the minimum known to be necessary for hydrotropic activity, i.e., at least 25-30 percent by weight, more usually ca 40 percent by weight. Preferred concentration ranges in the range 30-60 percent have variously been suggested in the aforesaid previous patents and only in an isolated instance, where cumene sulphonates stated were to be effective at concentrations down to 25 percent, has it been suggested that sulphonate salt concentrations below 30 percent could be used.

Besides specifying minimum aqueous sulphonate salt concentrations the aforesaid previous patents have also stipulated that. as a separate parameter, the ratio of sulphonate salt to soapstock present (or of free fatty acid in the original oil) must fall within a given range. British Pat. No. l,002,974 suggested as a rough guide a range of from 1-3 percent of 100 percent hydrotrope per unit of fatty acid value in the crude oil. In the case of the normally preferred hydrotrope, sodium xylene sulphonate, this is equivalent to a range of molar ratios of from 8.1:1 to 2.721 of sulphonate salt to soap. West German OLS No. 18 08 443 discloses that molar ratios of down to 1:1 may be employed where the free fatty acid in the crude oil has a high unsaturated content. Attempts by us to use sulphonate salt to soapstock molar ratios of less than 111, with the aqueous sulphonate salt concentration at or above the prescribed minimum of 30 percent have resulted in incomplete separation and occulsion of oil into the aqueous phase.

We have now discovered that it is, in fact, possible to maintain adequate phase separation using sulphonate salt to soap molar ratios of less than lzl if at the same time the aqueous concentration of the sulphonate salt is also reduced. By this means the sulphonate salt to soap molar ratio may in some cases be lowered to a value as low as ea. 0.l:l. using an aqueous concentration down to 3 percent sulphonate salt. This discovery is doubly surprising, firstly in that the sulphonate salt can function in concentrations considerably below those previously thought necessary and well outside the range for hydrotropic activity and, secondly, in that there is a hitherto unrecognized connection between the sulphonate salt concentration and the sulphonate salt to soap molar ratio.

The aforesaid discovery is of great utility in that it allows the quantities of sulphonate salt employed to facilitate phase disengagement in the alkaline glyceride oil refining process to be reduced far below the values previously thought to be the minima with the result that it becomes possible to operate economically a sulphonate asisted process wherein sulphonate is not recycled but is discarded after recovery of free fatty acids. This affords a considerable simplification in operating procedures.

We believe that these surprising observations may be explained on the assumption that the observed improvement in the separation of aqueous and oily phases when the sulphonate salts are present is not, as had been thought, a result of a hydrotropic increase in the aqueous solubility of the soap but a direct effect on the solubility of the oil in the aqueous phase, which effect is unconnected with the solubility ofthe soap. A further possibility is that the presence of the sulphonate salt brings about an alteration in the viscosity of the aqueous phase which discourages oil/aqueous emulsitication.

It is also clear that the action of the sulphonate salt is not by virtue of a normal surface active effect since, as in the processes of the aforesaid previous patents, only those sulphonates are effective which have little or no surfactant activity, i.e., lower alkyl aryl sulphonates. Higher alkyl aryl sulphonates such as sodium octylbenzene sulphonate which have occasionally been suggested for use in glyceride oil refining have no beneficial effect but on the contrary render phase separation very difficult.

Accordingly, the invention provides a process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali, together with an alkali metal. alkaline earth metal or ammonium salt of a phenyl or alkylphenyl sulphonic acid containing not more than 3 alkyl substituents having not more than 4 carbon atoms in the aggregate, the aqueous concentration of the sulphonate salt, being from 3 to l5 w/w and the molar ratio of sulphonate salt to soap present being from 0.l:l to l:l; allowing the mixture formed to separate'into an oily layer and an aqueous layer containing in solution the soap derived from the free fatty acid present in the crude oil and removing the aqueous layer.

Glyceride oils which may be treated by the process of the invention are any naturally occuring glyceride oils including vegetable and marine oils and animal oils including tallows. The alkali used for refining will normally be sodium hydroxide but may be any other which has previously been used or suggested such as potassium hydroxide or sodium carbonate. The invention may also be applied to mixtures of preformed soapstocks containing large amounts of glyceride oil such as arise during alkaline refining processes in which sulphonate salts are not used. In this aspect the process of the invention can be regarded as an improvement of that of West German OLS No. 17 67 814.

The possible values of sulphonate salt concentrations and sulphonate salt to soap molar ratios which may be used are interdependent and may lie within ranges of 3 to w/w concentration and 0.l:1:1 molar ratio. The minimum concentrations and ratios vary somewhat with the nature of the soap and the temperature and, to a lesser extent with the nature of the oil. Concentrations and ratios below the minima lead to the formation of oil/water emulsion.

The maximum usage at which it remains economic not to recycle sulphonate will vary but the preferred concentrations from the point of view of obtaining the best phase system consistent with economics will generally be in the range 4 to 9 percent sulphate salt and the preferred sulphonatersoap molar ratios will be from 0.25:1 to 0.5: l more especially 0.25:1 to 0.35:1, higher ratios being used with higher concentrations. Particularly effective phase separation is achieved at these values.

The ranges of values of the maximum ratio for given sulphonate concentrations vary somewhat with the soap concerned. We have determined a number of values of the maximum possible sulphonate salt to soap molar ratios for maintaining a one phase isotropic system at various sulphonate salt aqueous concentrations and at 80C. The systems considered were three components sodium xylene sulphonate/soap/water mix tures, the soaps being sodium oleate, sodium laurate and sodium stearate respectively. If, as is likely to be the case, the crude oil contains a mixture of free fatty acids, these determinations allow a general prediction to be made of the likely limiting values of sulphonate salt to soap ratios and sulphonate salt concentrations for any projected refining system in which the type of soap to be treated is known. If necessary the limiting values may then be confirmed by simple experiment. The details of the aforesaid determinations are as follows:

EXPERIMENT A series of mixtures of sodium xylene sulphonate, soap and water in various proportions were made up in separating funnels and held at 80C for 24 hours with gentle agitation so as to obtain a homogeneous aqueous solution phase in equilibrium with solid. The solution formed was then separated from the solid and analysed for soap and sodium xylene sulphonate content. The soap content was determined by acidification of standard portions of the solution with hydrochloric acid, repeated extraction with ether and evaporation of the ether from the combined extracts to obtain a residue of free fatty acid which was weighed.

Sodium xylene sulphonate contents were analysed by controlled dilution ofa standard portion of the solution with water to a concentration of about 0.3g sodium xylene sulphonate per 1i. and comparison of the Uv absorption intensifies of the diluted solution at 2672805 and 300 mN with calibrations obtained from a solution of known concentration.

Three soaps were used, sodium laurate, sodium stearate and sodium oleate. The analyses of the solutions obtained for each soap are given in-Tables I. 11 and 111. Table l: Limiting concentrations for homogeneous solutions in sodium xylene sulphonate/sodium laurate/- water systems at C.

Sodium laurate Sodium xylene Molar ratio Table I1: Limiting concentrations for homogeneous solutions in sodium xylene sulphonate/sodium stearate/- water systems at 80C.

Molar ratio sulphonatezsoap Sodium Stearate concentrations (w/w 71) Sodium xylene sulphonate concentrations Table III: Limiting concentrations for homogeneous solutions in sodium xylene sulphonate/sodium oleate/water systems at 80C.

Sodium Oleate Sodium xylene Molar ratio concentrations (w/w 72) sulphonate sulphonate:soap

concentrations (w/w 21 Thus, at any given concentration of sodium xylene sulphonate noted in the Tables, operation at a sulphonatersoap molar ratio below that indicated will give a readily separable two-phase system, provided both concentration and ratio are above the minima hereinbefore specified. Similarly a maximum permissible concentration for operation at a molar ratio as noted in the Tables may be determined. Other values may be determined by extrapolation or interpolation and/or confirmed by simple experiment.

The actual values of the sulphonate concentration and sulphonate/soap ratios to be employed in the process of the invention will primarily depend upon process economics and plant capacity.

' ing difficulties in the work-up of the recycle stream. It

is an advantage of the invention that the lower sulphonate concentrations used mitigate this problem. It has in fact been discovered that there is a critical sulphonate concentration in the region of 25 30 percent, depending upon the fatty acid concerned below which the fatty acid solubility shows a sharp drop. This discovery forms a further surprising feature of the invention and a novel refining process as hereinbefore described wherein the separated aqueous phase is subsequently acidified to liberate free fatty acid and the free fatty the thus diluted acid with the soapstock material may advantageously be used as described in application Ser. No. 60166/69 ion British Pat. No. 1,286,878.

If desired crystallization and filtration of sodium sulphate from the acid-free aqueous stream may be effected by straightforward cooling, e.g., evaporative cooling say to 25C. As described in our copending application Ser. No. 22164/70 it has been found that crystallization and filtration may be ameliorated if the mother liquor is neutralized to a pH7-8 and then passed through a rudimentary phase separator acid is then separated constitutes a further aspect of the invention.

Preferred sulphonate salts for use in the novel process are sodium salts, particularly those of benzene, toluene, xylene, hemimellitene, pseudocumene, mesitylene, ethylbenzene, n-propylbenzene, cumene and pcymene sulphonic acids. Particularly good results are obtained with sodium toluene and sodium xylene sulphates especially as regards the soapstock acidification procedure wherein these sulphonates appear to solubilise less fatty acid than do other sulphonates and so ease the later problems involved in crystallising sodium sulphate from the sulphonate recycle stream. Sodium xylene sulphonate is most preferred.

The temperature at which the novel process is carried out may be as normally used in glyceride oil refining processes, say 60 to 90C. The temperature affects the solubility of the soap in the aqueous phase and thus the limiting value of the sulphonate salt to soap molar ratio which may be used. 60 to 90C has been found to be a generally convenient operating temperature,

80C is usually preferred.

After separation the aqueous and oily phases may be treated by known means. The oily layer may be used without further treatment or may be washed and otherwise treated, e.g., by drying, bleaching or deodorization before use. The aqueous layer may either be discarded or treated to recover free fatty acids and sulphonate salt therefrom. The latter operation may be conducted by known means, i.e., acidification with sulphuric acid followed by separation of the free fatty acid and aqueous phases formed. If desired crystallization and filtration of sodium sulphate from the aqueous phase may then be effected followed by recycle of the mother liquor to the refining stage.

The acidification step may be performed in known fashion, acidifying say to pH2.5 to 3.5 desirably using sulphuric acid, preferably at high concentration, say 96 percent or greater strength. A particularly efficient mode of acidification is that described in co-pending application Ser. No. 60166/69 wherein, before addition to thesoapstock material the acid is prediluted with recycled aqueous phase resulting from the acidification. The ratio of recycle to product may well depend upon the precise operating condition used but will often be in the range 2-4z1. A system comprising two venturi type mixers for mixing acid with aqueous recycle and prior to crystallization to separate off a more buoyant layer. This serves to remove from the stream small quantities of solubilised glyceride oil which would otherwise interfere with the crystallization, particularly evaporative crystallization.

After crystallization of sodium sulphate and filtration the filtrate, containing dissolved sulphonate salt, may be recycled to the refining stafe if desired.

Several alternative schemes for working up the aqueous acidified soapstock stream may be used. For example it may be possible to subject only a fraction of it to sodium sulphate crystallization prior to recycle and to conduct the rest directly to the refining stage after neutralisation. Alternatively, the low sulphonate salt concentrations made possible by the invention may make it economic to maintain the sodium sulphate concentration in the process at an equilibrium value by discarding a proportion of the aqueous stream continuously or intermittently.

The invention is illustrated by the following examples wherein all parts are by weight.

EXAMPLE A fish oil blend containing 3.5 percent by weight of free fatty acid (as oleic acid) was continuously neutralised at -90C with sodium hydroxide solution containing a 10 percent excess of sodium hydroxide over that theoretically required to neutralise the free fatty acid. Neutralisation was conducted in the presence of sodium xylene sulphonate at a concentration of 6 percent based on the water present and of sulphonate salt. The molar ratio to the free fatty acid was 0.25:1.

An oily layer and an aqueous soapstock layer disengaged readily. The aqueous layer, containing dissolved sulphonate salt, was analysed for free fatty acid content and discarded.

The oily layer, which had a free fatty acid content of less than 0.1 percent w/w (described) was washed with water and dried under vacuum to give substantially pure product. The refining factor was 1.53. The ratio ofthe weight of fatty acid obtained in the aqueous layer (expressed asfree fatty acid) to that estimated by analysis to be present in the crude oil before refining was 1.45.

We claim:

11. A process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali, together with an alkali metal, alkaline earth metal or ammonium salt of a phenyl or alkylphenyl sulphonic acid containing not more than 3 alkyl substituents having not more than 4 carbon atoms in the aggregate, the concentration of sulphonate salt being from 4 to 9 percent w/w and the molar ratio of sulphonate salt to soap present being from 0.25:1 to 0.5: 1 allowing the mixture formed to separate into an oily layer and an aqueous layer containing in solution the free fatty acid present in the crude oil and removing the aqueous layer.

2. A process according to claim 1 wherein the sulphonate salt is an alkali metal salt.

3. A process according to claim 2 wherein the sulphonate salt is sodium xylene sulphonate or sodium toluene sulphonate.

4. A process according to claim 3 wherein the removed aqueous layer is subsequently acidified with acid to liberate free fatty acid therefrom and the free fatty acid is then separated.

5. A process according to claim 4 wherein before addition to the removed aqueous soap-containing material the acid is prediluted with recycled aqueous phase resulting from the acidification.

6. A process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali. together with sodium xylene sulphonate or sodium toluene sulphonate, the concentration of said sulphonate being from 4 to 9 percent w/w and the molar ratio of said sulphonate to soap present being from 0.1:] to 1:1; allowing the mixture formed to separate into an oily layer and an aqueous layer containing in solution the free fatty acid present in the crude oil and removing the aqueous layer.

7. A process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali, together with sodium xylene sulphonate or sodium toluene sulphonate. the concentration of sulphonate salt being from 4 to 9 percent w/w and the molar ratio of said sulphonate to soap present being from 0.25:1 to 0.511; allowing the mixture formed to separate into an oily layer and an aqueous layer containing in solution the free fatty acid present in the crude oil and removing the aqueous layer.

* l l l= 

1. A PROCESS OF REFINING GLYCERIDE OILS WHICH COMPRISES MIXING THE OIL WITH A DILUTE AQUEOUS SOLUTION OF AN ALKALI, TOGETHER WITH AN ALKALI METAL, ALKALINE EARTH METAL OR AMMONIUM SALT OF A PHENYL OR ALKYLPHENYL SULPHONIC ACID CONTAINING NOT MORE THAN 3 ALKYL SUBSTITUENTS HAVING NOT MORE THAN 4 CARBON ATOMS IN THE AGGREGATE, THE CONCENTRATION OF SULPHONATE SALT BEING FROM 4 TO 9 PERCENT W/W AND THE MOLAR RATIO OF SULPHONATE SALT TO SOAP PRESENT BEING FROM 0.25:1 TO 0.5:1; ALLOWING THE MIXTURE FORMED TO SEPARATE INTO AN OILY LAYER AND AN AQUEOUS LAYER CONTAINING IN SOLUTION THE FREE FATTY ACID PRESENT IN THE CRUDE OIL AND REMOVING THE AQUEOUS LAYER.
 2. A process according to claim 1 wherein the sulphonate salt is an alkali metal salt.
 3. A process according to claim 2 wherein the sulphonate salt is sodium xylene sulphonate or sodium toluene sulphonate.
 4. A process according to claim 3 wherein the removed aqueous layer is subsequently acidified with acid to liberate free fatty acid therefrom and the free fatty acid is then separated.
 5. A process according to claim 4 wherein before addition to the removed aqueous soap-containing material the acid is prediluted with recycled aqueous phase resulting from the acidification.
 6. A process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali, together with sodium xylene sulphonate or sodium toluene sulphonate, the concentration of said sulphonate being from 4 to 9 percent w/w and the molar ratio of said sulphonate to soap present being from 0.1:1 to 1:1; allowing the mixture formed to separate into an oily layer and an aqueous layer containing in solution the free fatty acid present in the crude oil and removing the aqueous layer.
 7. A process of refining glyceride oils which comprises mixing the oil with a dilute aqueous solution of an alkali, together with sodium xylene sulphonate or sodium toluene sulphonate, the concentration of sulphonate salt being from 4 to 9 percent w/w and the molar ratio of said sulphonate to soap present being from 0.25:1 to 0.5:1; allowing the mixture formed to separate into an oily layer and an aqueous layer containing in solution the free fatty acid present in the crude oil and removing the aqueous layer. 